The present invention concerns leak detection and more particularly the testing of containers such as auto fuel tanks to identify any tanks having leaks.
It is often necessary to inspect vessels such as gasoline fuel tanks during their production to insure that even very slight leaks are not present. A common test procedure is to pressurize the interior of the tank with a trace gas mixture and provide an arrangement for detecting the presence of trace gas in a cavity surrounding the tank, to thereby establish whether or not a leak is present in the tank being tested.
See for example, U.S. Pat. No. 3,813,923 which shows such a test apparatus.
In the production of fuel tanks in the very high volumes of the automotive industry, the time required for completion of the leak test is of crucial significance. Since the time to carry out such test is proportional to the differential pressures across the tank wall at which the tests are run, and since very slight leaks must be detected for such applications, the leakage rate will require excessively long test periods for reliable testing.
On the other hand, typical fuel tanks, cannot withstand even moderate differential pressures without damage due to the resulting overexpansion.
The dimensional variations normally encountered during manufacture of the fuel tanks precludes the manufacture of a rigid surrounding chamber to enclose the tank, since excessive clearance spaces therebetween would allow such damage to occur as the tank expanded into the clearance spaces.
One solution to the problem of accommodating dimensional variations in the fuel tanks while protecting the tank from the damaging effects of expanding under excessive differential pressures is described in the aforementioned U.S. Pat. No. 3,813,923. In this patent, surrounding diaphragms are placed within the test fixture and the exterior of the diaphragms are pressurized during the application of a vacuum to the space between the diaphragms and the tank, and pressurized gas is communicated to the interior of the tank. The surrounding diaphragms apply a counteracting force to neutralize the effect of the high differential pressure created by the surrounding vacuum to thereby protect the tank from pressure-induced damage.
See also U.S. Pat. No. 4,055,984 to Marx which discloses surrounding a container to be leak tested with a flexible test housing which does not involve the pressurization of the exterior of the flexible housing.
Fuel tanks normally have two or more openings which must be sealed during testing, such as the filler opening and the fuel line outlet, and also typically an electronic fuel level detector package is mounted within another opening in the bottom of the gasoline tank.
In order to achieve the desired goal of rapid testing, it is highly desirable to provide for automatic resealing of such openings as by an automatically operated sealing arrangement incorporated in the test fixturing. This eliminates a separate installation or assembly step in the leak detection test procedure.
In the arrangements of the aforementioned U.S. patents, a flexible housing surrounding the fuel tank cannot provide a fixturing for sealing of these openings due to the lack of structural support available from the flexible housings. This also necessitates a separate fixturing for supporting the weight of the tank during testing. The use of fixturized sealing tank arrangements would necessitate accurate location of the tank which also cannot be achieved by a flexible housing.
In typical fuel tanks, the tank is formed by two opposing members having aligned flanges which are welded, brazed or otherwise secured together to seal the tank interior. A very high proportion of the leaks experienced in such tanks occur in the flange region. On the other hand, the flange region is much less susceptible to failure upon exertion of the relatively high differential pressures thereacross even when unsupported. It is thus desirable that the reliability of the leak testing be extremely high for detecting leaks in the flange regions of the tanks.
Accordingly, it is an object of the present invention to provide a method and fixture for leak detection testing on a production basis for such containers as auto fuel tanks in which the application of excessively high forces on the tank from the effects of differential pressures are avoided.
It is another object of the present invention to provide a fixturing for leak detection in which sealing arrangements for tank openings are carried by the fixturing and includes a housing in which the gasoline tank is accurately located for proper operation of such sealing arrangements.
It is yet another object of the present invention to provide a fixturing for leak detection of fuel tanks and the like in which a single fixture housing is employed to define a clearance cavity between the tank and the housing for carrying out a pressure leak test of the tank, which does not result in differential pressure-induced damage to the tank and yet allows a relatively high differential pressure to be experienced by the tank to insure rapid leak detection testing.
It is still another object of the present invention to provide a method and fixture for leak testing of flanged containers such as fuel tanks which have a maximum reliability for detecting leaks in the flange regions thereof.